Image combiner and image display unit

ABSTRACT

During use, a plate-form part  5  which is constructed from an optical material and which corresponds to a spectacle lens is positioned in front of the eye of the user which is disposed in the vicinity of the exit pupil P of an image combiner  1 . The combiner  1  causes light from an image display element  2  to be superimposed on light that is transmitted through the plate-form part  5  so as to pass through the thickness of the plate-form part  5  from the front of the plate-form part  5 , and conducts this light to the eye. The light from the image display element  2  reaches the eye of the user after being diffracted and reflected by a reflective type HOE  6  inside the plate-form part  5 . The wavelength at which the diffraction efficiency shows a maximum value when the chief rays that are emitted from the center of the display part of the image display element  2  are diffracted and reflected by the reflective type HOE  6  and the wavelength at which the diffraction efficiency shows a maximum value when the chief rays that are emitted from the peripheral portions of the display part in a specified direction are diffracted and reflected by the reflective type HOE  6  are substantially different. As a result, it is possible to improve the image quality of the display images that are obtained in cases where the center of the pupil of the eye of the user deviates from the center of the exit pupil of the image combiner.

This is a continuation of PCT International Application No.PCT/JP2003/009430 filed on Jul. 25, 2003, which is hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates to an image combiner which makes itpossible for the user to view an image based on light from the frontsuch as the outside world and a display image that is superimposed onthis first image, and an image display device such as a head-mounteddisplay using this image combiner.

BACKGROUND ART

In the past, for example, the image display devices disclosed inJapanese Patent Application Kokai No. 2000-352689 and Japanese PatentApplication Kokai No. 2001-264682 have been known as so-calledsee-through type head-mounted image display devices (head-mounteddisplays) which allow the user to view a display image superimposed on aview of the outside world while observing the conditions of this outsideworld. Furthermore, Japanese Patent Application Kokai No. 2001-264682discloses not only a see-through type head-mounted image display device,but also an image display device that is not used as a see-through typedevice (i.e., that conducts only light from an image display element tothe eyes of the user without superimposing other light from the outsideworld or the like on this light from the image display element) whilehaving substantially the same construction as such a see-through typedevice; an example in which this image display device is contained inthe flipper part of a portable telephone is also disclosed.

In these image display devices, a reduction in size and weight isachieved by using a reflective type hologram optical element. Such areflective type hologram optical element is superior in terms ofwavelength selectivity, and can selectively diffract and reflect onlylight in an extremely limited wavelength region. Accordingly, in caseswhere a see-through type image display device is constructed, loss ofthe amount of light that is transmitted from the outside world or thelike by means of a reflective type hologram optical element can beconspicuously reduced.

Furthermore, in these image display devices, the exit pupil of the imagecombiner is formed so that this pupil substantially coincides with thepupil of the eye of the user in the use state, and a reflective typehologram optical element which is manufactured so that the position ofone light source (the reference light source) of the two light sourcesthat are used to expose the reflective type hologram optical elementduring the manufacture of this element is caused to coincidesubstantially with the position of the exit pupil of the image combineris used as the reflective type hologram optical element (paragraph No.25 of Japanese Patent Application Kokai No. 2000-352689 and paragraphNo. 37 of Japanese Patent Application Kokai No. 2001-264682). In thesepatent applications, the following effect is described: namely, by usinga reflective type hologram optical element which is manufactured withthe position of the reference light source during manufacture disposedin the position of the pupil of the user, the exposure light duringmanufacture and the observation light during use substantially coincide,so that the diffraction efficiency of the reflective type hologramoptical element during use can be improved to the maximum extent(paragraph No. 25 of Japanese Patent Application Kokai No. 2000-352689and paragraph No. 37 of Japanese Patent Application Kokai No.2001-264682).

Furthermore, in these image display devices, a liquid crystal displayelement is generally used as the image display element in order toachieve a reduction in size and weight, and an LED, which is a compactand inexpensive light source, is used as the light source thatilluminates this image display element.

However, in these conventional image display devices, although a gooddisplay image can be viewed in cases where the center of the pupil ofthe eye of the user and the center of the exit pupil of the imagecombiner coincide, the display screen gradually becomes darker as thecenter of the pupil of the eye of the user moves toward the periphery ofthe exit pupil of the image combiner from the center of this exit pupil,and the display image appears to be blurred, so that the image is notalways sufficient in terms of image quality. Furthermore, during actualuse, it can frequently happen that the center of the pupil of the eye ofthe user deviates from the center of the exit pupil of the imagecombiner.

DISCLOSURE OF THE INVENTION

The present invention was devised in the light of such circumstances; itis an object of the present invention to provide an image display devicewhich can improve the image quality of the display image in cases wherethe center of the pupil of the eye of the user deviates from the centerof the exit pupil of the image combiner, while achieving a reduction insize and weight by using a reflective type hologram optical element, andan image combiner that can be used in such an image display device orthe like. Furthermore, in the following description, there may beinstances in which the hologram optical element is referred to as an“HOE.”

It is known that the diffraction characteristics of a reflective typeHOE, and especially of a reflective volume type HOE, have a sharpwavelength selectivity and broad angular characteristics. Specifically,diffracted light can be obtained in a specified direction at a maximumefficiency with respect to reproduced light incident at an angle and awavelength that satisfy the Bragg condition; however, there arecharacteristics in which the diffraction efficiency drops abruptly whenthere is a departure from the Bragg condition with respective to theincident wavelength, and on the other hand, there are characteristics inwhich the diffraction efficiency gradually decreases in cases where theangle of incidence departs from Bragg angle incidence.

As a result of these characteristics, such a reflective type HOE hasbecome known as an element suitable for use in an image combiner that iscapable of performing an image display having a wide angle of viewwithout losing the brightness of light from the outside world.

However, this is an argument that is limited solely by the value of thediffraction efficiency in the case of illumination by light of a singlewavelength; research has not proceeded as far as the wavelengthcharacteristics of light that is diffracted in cases where illuminationis actually performed using illuminating light that has a bandwidth.

The present inventor investigated the diffraction characteristics of areflective type HOE in a case where the angle of incidence deviates fromBragg angle incidence, and discovered that when the angle of incidencevaries, the wavelength that is diffracted at a maximum efficiencyvaries. Similarly, furthermore, the inventor also discovered that whenthe diffracted light from an HOE is observed from different directions,the wavelength at which the diffraction efficiency shows the highestvalue varies. This point will be described below.

Diffraction by a reflective type HOE shows a maximum diffractionintensity in a direction that conforms to the Bragg conditional formula.The Bragg conditional formula in a reflective type HOE is expressed byEquation (1) and Equation (2) shown below. The intensity of the lightthat is diffracted in a direction that simultaneously satisfies Equation(1) and Equation (2) below shows a maximum value.1/λ_(R)(sinθ_(O)−sin θ_(R))=1/λ_(C)(sinθ_(I)−sinθ_(C))  (1)1/λ_(R)(cosθ_(O)−cosθ_(R))=1/λ_(C)(cosθ_(I)−cosθ_(C))  (2)

Here, the left side in Equation (1) and Equation (2) indicates the stateduring the manufacture of the reflective type HOE, λ_(R) indicates theexposure wavelength, θ_(O) indicates the angle of incidence of theobject light during exposure with respect to the normal of the plane ofthe hologram, and θ_(R) indicates the angle of incidence of thereference light during exposure. Furthermore, the right side in Equation(1) and Equation (2) indicates the state during use of the reflectivetype HOE, λ_(C) indicates the dominant wavelength of diffraction, θ_(C)indicates the angle of the line of sight with respect to the normal ofthe plane of the hologram as measured from the center of the plane ofthe hologram, and θ_(I) indicates the angle of incidence of theilluminating light (corresponding to the line of sight) on the plane ofthe hologram.

This is shown graphically in simplified model form in FIG. 25.Furthermore, in FIG. 25(b), PC indicates the position of the center ofthe pupil of the eye of the user. When ray tracing is performed, thelight rays are traced from the position PC; accordingly, the orientationof the light rays in FIG. 25(b) is shown as coinciding with the case ofray tracing; however, the actual orientation of the light rays is theopposite orientation.

Here, if the wavelength λ_(C) which has a diffraction intensity and theangle of incidence θ_(I) of the illuminating light are determined fromthe conditions during the manufacture of the HOE and the angle θ_(C) ofthe line of sight on the basis of Equation (1) and Equation (2), thevalues shown in Equation (3) and Equation (4) below are obtained.$\begin{matrix}{\lambda_{C} = {{- \left\lbrack {{\left( {{\sin\quad\theta_{O}} - {\sin\quad\theta_{R}}} \right)\sin\quad\theta_{C}} + {\left( {{\cos\quad\theta_{O}} - {\cos\quad\theta_{R}}} \right)\cos\quad\theta_{C}}} \right\rbrack} \times}} & (3) \\{\quad{{2/\left\lbrack {\left( {{\sin\quad\theta_{O}} - {\sin\quad\theta_{R}}} \right)^{2} + \left( {{\cos\quad\theta_{O}} - {\cos\quad\theta_{R}}} \right)^{2}} \right\rbrack} \times \lambda_{R}}} & \quad \\{\theta_{I} = {\arcsin\left\{ {{\lambda_{C}/\lambda_{R}} \times \left( {{\sin\quad\theta_{O}} - {\sin\quad\theta_{R}}} \right)\sin\quad\theta_{C}} \right\}}} & (4)\end{matrix}$

Here, the intensity of diffracted light in cases where there is adeviation from the Bragg condition is not zero, but rather dropsaccording to the amount of this deviation. The manner in which thisintensity drops varies according to the thickness of the phase volumetype hologram material and the amount of variation in the refractiveindex; this intensity drops more abruptly as the thickness increases, oras the amount of variation in the refractive index increases. In otherwords, the wavelength selectivity becomes sharper, so that thecontribution of the diffraction indicated by Equation (2) becomesgreater.

In actuality, therefore, the wavelength λ_(C) in Equation (3) is thewavelength at which the diffraction intensity shows a maximum value, andlight in a wavelength band having a bandwidth in the vicinity of thiswavelength is also diffracted as the diffracted light. Accordingly,λ_(C) in Equation (3), which satisfies the Bragg condition formula, iscalled the dominant diffraction wavelength.

Here, the behavior of the dominant diffraction wavelength λ_(C) and theangle of incidence θ_(I) of the illuminating light corresponding to theline of sight was investigated by varying the angle θ_(C) of the line ofsight under the following conditions: exposure wavelength λ_(R)=476 nm,angle of incidence θ_(R) of reference light=30°, angle of incidenceθ_(O) of object light=150°, reflective type HOE in air. The respectiveangles were measured in counterclockwise rotation from the positivedirection of the normal of the reflective type HOE. The results obtainedare shown in Table 1 below. As is seen from Table 1, the dominantdiffraction wavelength λ_(C) shifts by approximately ±9 nm when theangle θ_(C) of the line of sight varies by ±5 degrees. TABLE 1 DominantAngle of Angle θ_(C) of diffraction incidence θ_(I) of line of sightwavelength λ_(C) illuminating light (deg) (nm) (deg) 25 484.5 155 30476.0 150 35 466.4 145

Here, when Equation (3) is rewritten as the ratio λ_(C)/λ_(R) of thedominant diffraction wavelength λ_(C) to the exposure wavelength λ_(R)(relative dominant diffraction wavelength), Equation (5) shown below isobtained: $\begin{matrix}{{\lambda_{C}/\lambda_{R}} = {{- \left\lbrack {{\left( {{\sin\quad\theta_{O}} - {\sin\quad\theta_{R}}} \right)\sin\quad\theta_{C}} + {\left( {{\cos\quad\theta_{O}} - {\cos\quad\theta_{R}}} \right)\cos\quad\theta_{C}}} \right\rbrack} \times}} & (5) \\{\quad{2/\left\lbrack {\left( {{\sin\quad\theta_{O}} - {\sin\quad\theta_{R}}} \right)^{2} + \left( {{\cos\quad\theta_{O}} - {\cos\quad\theta_{R}}} \right)^{2}} \right\rbrack}} & \quad\end{matrix}$

FIG. 26 shows a graph of the variation in the value of the relativedominant diffraction wavelength λ_(C)/λ_(R) indicated in Equation (5)which was obtained in a case where the difference (θ_(C)−θ_(R)) of theangle θ_(C) of the line of sight relative to the angle of incidenceθ_(R) of the reference light during exposure was varied with the angleof the exposure light as a parameter. As is seen from FIG. 26, the valueof the relative dominant diffraction wavelength λ_(C)/λ_(R) also departsfrom 1 as the difference in angles (θ_(C)−θ_(R)) departs from 0.Accordingly, it is seen that the wavelength shift increases as thedifference (θ_(C)−θ_(R)) between the angle θ_(C) of the line of sightand the angle of incidence θ_(R) of the reference light during exposureincreases. Furthermore, for convenience of description, this phenomenonis called the “wavelength shift phenomenon.”

In the conventional image display devices described above, a reflectivetype hologram optical element is used which is manufactured with theposition of the reference light source used for exposure duringmanufacture caused to coincide with the position of the exit pupil ofthe image combiner. Specifically, the position of the reference lightsource during exposure is defined as the pupil position of the playbacksystem. Accordingly, while the difference between the angle of incidenceof the reference light during exposure and the angle of the line ofsight is substantially zero at all angles of view for the chief raysduring playback, a difference is generated between the angle θ_(C) ofthe line of sight and the angle of incidence θ_(R) of the referencelight for light rays (marginal rays) passing through positions thatdeviate from the center in the exit pupil of the image combiner.Consequently, a wavelength shift occurs in the marginal rays duringplayback as a result of the wavelength shift phenomenon described above.

Furthermore, in the conventional image display devices described above,it has been ascertained that the reason that the display screen becomesdarker as the center of the pupil of the eye of the user moves towardthe periphery of the exit pupil of the image combiner from the center ofthis exit pupil is as follows: namely, the optical intensity at the exitpupil is combination of the incident light intensity and the diffractionefficiency. Here, the wavelength characteristic of incident lightintensity is uniquely decided by a light source.

On the other band, the wavelength characteristic of diffractionefficiency changes depending on the position in the exit pupil becauseof wavelength shift phenomenon as described above. Therefore, in theperiphery of the pupil, the intensity decreases according to thewavelength characteristic of incident light intensity. Moreover, it hasbeen ascertained that the reason that the image appears to be blurred isas follows: namely, since the diffraction wavelength varies as theperiphery of the pupil is approached, a transverse chromatic aberrationis generated.

For the image display devices of several embodiments described inJapanese Patent Application Kokai No. 2000-352689 and Japanese PatentApplication Kokai No. 2001-264682, the present inventor concretelydetermined the variation in the diffraction wavelength described aboveand the resulting amount of transverse chromatic aberration byperforming ray tracing toward the image display element (image formingmember such as a liquid crystal display element) from the pupil of theobserver (user). The results obtained will be described below.

In the case of Embodiment 3 described in Japanese Patent ApplicationKokai No. 2000-352689, a reflective type hologram optical element isused which is manufactured with the position of the reference lightsource used for exposure during manufacture and the position of the exitpupil of the image combiner caused to coincide. Accordingly, the Braggcondition is satisfied with respect to the chief rays, i.e., light raysdirected toward various points of the image plane from the center of thepupil. Consequently, light at the same wavelength (532 nm) as theexposure wavelength is reflected and diffracted at a high diffractionefficiency over all angles of view; however, the diffraction efficiencyof light rays that are incident from the pupil coordinate y=1.5 (the yaxis is taken in the upward direction in the plane of the page) shows amaximum value at 527 nm. Conversely, the diffraction efficiency of lightrays that are incident from the position of the pupil coordinate y =−1.5shows a maximum value at 537 nm. In other words, it is seen that thediffraction wavelength shifts by ±5 nm as the periphery of the pupil isapproached. Here, the pupil coordinates refer to positional coordinateswithin the plane of the pupil; the center of the pupil is taken as theorigin, and the units are set as millimeters.

Here, in cases where a green LED which has an emission peak in thevicinity of 532 nm is used as the illuminating light source, if theemission characteristics are set at (for example) approximately 20 nm interms of the full width at half maximum, the emission intensity at 527nm is 0.5, and the emission intensity at 537 nm is 0.5, where theemission intensity at 532 nm is taken as 1.

Accordingly, at positions where the pupil coordinate y=+1.5, even if thediffraction efficiency of the reflective type HOE is a high efficiencyof 90% or greater, the intensity of the illuminating light is 0.5compared to the center since the diffraction wavelength is shifted by +5nm; as a result, the observed image becomes darker.

Furthermore, if the transverse chromatic aberration is calculated, then,relative to the y coordinate y=0.0 on the image plane of light rays thatare incident at an angle of view of 0° from the center of the pupil at awavelength of 532 nm, the height on the image plane of light rays thatare incident from a pupil coordinate y=1.5 at a wavelength of 527 nm isy=−0.10, and the height on the image plane of light rays that areincident from a pupil coordinate y=−1.5 at a wavelength of 537 nm isy=0.12, so that a transverse chromatic aberration of 0.1 mm or greateris generated.

Assuming that a {fraction (1/4)} inch (4.8×3.6 mm) QVGA (320×240 pixels)liquid crystal display device is placed on the image plane, i.e., thesurface of the image forming member, then the size of one pixel is 0.015mm square, and the chromatic aberration of magnification described abovehas a large value corresponding to 7 to 8 pixels.

Specifically, as a result of the chromatic aberration arising from thiswavelength shift, the image appears to be blurred as the periphery ofthe pupil is approached.

The present inventor conducted further research based on the resultsobtained in an elucidation of the causes of the problems encountered insuch a conventional image display device, and investigated the use of areflective type HOE manufactured with the position of the referencelight source during exposure moved to the position of the playback falseimage (this position is ordinarily a position that is separated from theexit pupil of the image combiner by a distance of 1 m to infinity)instead of a reflective type HOE manufactured with the position of thereference light source during exposure and the position of the pupil ofthe playback system set as the same position.

When a reflective type HOE is used which is manufactured with theposition of the reference light source during exposure moved to theposition of the playback false image, as long as the light rays have thesame angle of view, the difference (θ_(C)−θ_(R)) between the angle θ_(C)of the line of sight and the angle of incidence θ_(R) of the referencelight is smaller than in a conventional device, even for light rayspassing through any position within the exit pupil of the imagecombiner, regardless of whether these light rays are chief rays ormarginal rays.

Accordingly, the intensity distribution in the ray bundle section, whichis constituted from light rays, become uniform. And the dominantdiffraction wavelength about the rays at the center of the angle of viewis substantially equal to the exposure wavelength.

Accordingly, even if the center of the pupil of the eye of the userdeviates from the center of the exit pupil of the image combiner,darkening of the display image and apparent blurring of the displayimage are eliminated, so that the image quality in cases where thecenter of the pupil of the eye of the user deviates from the center ofthe exit pupil of the image combiner is greatly improved compared to thecase of the conventional image display devices described above.Consequently, the convenience of the device for the user is greatlyimproved.

Where [i] the wavelength at which the diffraction efficiency in a casewhere the light passes through a specified position after being emittedfrom the center of the display part of the image display means anddiffracted by the reflective type hologram optical element shows amaximum value in the respective wavelength regions described above isdesignated as λ_(o), [ii] the wavelength at which the diffractionefficiency of the light that passes through the same position as thespecified position mentioned above after being emitted from theperipheral portions of the display part of the image display means anddiffracted by the reflective type hologram optical element shows amaximum value in the respective wavelength regions is designated asλ_(y) and [iii] the wavelength at which the diffraction efficiency ofthe light that is propagated at a different position from the specifiedposition after being emitted from the center of the display part of theimage display means and diffracted by the reflective type hologramoptical element and in which the direction of sight with respect to thereflective type hologram optical element is the same direction as thedirection of propagation of the light that passes through the specifiedposition after being emitted from the center of the display part anddiffracted by the reflective type hologram optical element shows amaximum value in the respective wavelength regions is designated asλ_(z), the present invention is devised so that substantially the sameimage quality can be obtained even if the position of the pupil of theeye of the user should vary within the plane of the exit pupil, bysetting λ_(o) and λ_(z) at substantially the same wavelength.Consequently, since the conditions are such that the emission angles ofthe light following diffraction differ from each other, λ_(y) and λ_(o)show different values.

Accordingly, in the case of a reflective type HOE manufactured with theposition of the reference light source during exposure moved to aposition that is shifted from the position of the pupil of the playbacksystem toward the position of the playback false image, if thewavelength λ_(o) and wavelength λ_(y) are set so that these wavelengthsare different, there is no deterioration in the image quality even incases where the center of the pupil of the eye of the user deviates fromthe center of the exit pupil of the image combiner.

Here, if it is desired to achieve a certain degree of improvement in theimage quality in cases where the center of the pupil of the eye of theuser deviates from the center of the exit pupil of the image combiner,it is desirable that either Equation (6) or Equation (7) shown below besatisfied.1.013<λ_(y)/λ_(o)  (6)λ_(y)/λ_(o)<0.98  (7)

Furthermore, if the amount of the wavelength shift caused by the angleof view with respect to the emission spectrum width of the illuminatinglight source is excessively large, there is a danger that a drop in thequantity of light will occur in portions located within the screen.Accordingly, in order to prevent this, it is desirable that the emissionspectrum width of the illuminating light source and the wavelength shiftcaused by the angle of view be taken into consideration, and that theamount of the wavelength shift be controlled by causing the referencelight source to approach the vicinity of the pupil from the vicinity ofthe false image in cases where the emission spectrum width is narrow. Inconcrete terms, in cases where the light that is emitted from the imagedisplay means has only a single wavelength region component or aplurality of discrete wavelength region components, it is desirable thatEquation (8) shown below be satisfied when the full width at halfmaximum in the single wavelength region or the full width at halfmaximum of one of the plurality of wavelength regions is set as FWHM.0.2<|(λ_(y)−λ_(o))/FWHM|  (8)

Furthermore, the “0.2” on the left side of Equation (8) is based on theresults obtained by giving consideration so that the spectra of the halfbandwidths of the respective wavelength regions are also included in thefull width at half maximum of the spectrum of the light source, as aresult of taking into account the half bandwidth of the spectrum of thediffraction wavelength region centered on the wavelength λ_(y) and thehalf bandwidth of the spectrum of the diffraction wavelength regioncentered on the wavelength λ_(o).

The above was an investigation of the distance of the reference lightsource. However, the present inventor also investigated the angle ofincidence of the reference light source, and obtained the followingresults. Specifically, by appropriately setting the angle of incidenceof the reference light source, it is possible to correct the deviationof the wavelengths of the exposure light source and illuminating lightsource, so that the brightness center is always caused to coincide withthe screen center.

It is desirable that the wavelength of the exposure light source and thewavelength of the illuminating light source coincide; ordinarily,however, since a laser is used as the exposure light source and an LEDis used as the illuminating light source, and since the light generatingmeans are different in a laser and an LED, the wavelengths of the twolight sources do not always coincide. Accordingly, in cases where thereis some deviation, it was found that the reduction in light at the endsof the angle of view can be balanced by adjusting the angle of thereference light source so that the dominant diffraction wavelength atthe center of the angle of view and the dominant wavelength of theilluminating light source are caused to coincide.

With regard to the method used, the characteristic of the wavelengthshift caused by the angular difference between the reference light andthe playback incident light can be positively used, and the angle ofincidence of the reference light source can be shifted from thatdescribed above so that the dominant diffraction wavelength of the lightrays at the center of the angle of view coincides with the dominantwavelength of the illuminating light source instead of the exposurewavelength, thus shifting the dominant diffraction wavelength of thelight rays at the center of the angle of view of the playback systemfrom the exposure wavelength. The amount can be calculated in reversefrom Equations (3) and (4) described above. Specifically, the differencein the angle of incidence can be calculated so that the dominantdiffraction wavelength coincides with the dominant wavelength of theilluminating light source.

In concrete terms, if the angle of incidence (angle calculated in air)on the center of the reflective type hologram optical element from thelight source located on the side of the eye of the observer duringplayback (of the two light sources used to expose the reflective typehologram optical element during manufacture) is designated as θ1, andthe angle of reflection (angle calculated in air) at the reflective typehologram optical element of the light rays that are emitted from thecenter of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner is designatedas θ2, then the reduction in light at the ends of the angle of view canbe balanced in a state close to the center distribution if Equation (9)shown below is satisfied.0.8°<|θ1−θ2|  (9)

As was described above, the present invention can provide an imagedisplay device which is capable of achieving an improvement in the imagequality of the display image in cases where the center of the pupil ofthe eye of the user deviates from the center of the exit pupil of theimage combiner while achieving a reduction in size and weight by using areflective type hologram optical element, and can also provide an imagecombiner that can be used in such an image display device or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram which shows the construction of an image displaydevice constituting a first working configuration of the presentinvention, and (in schematic terms) the path of the light rays in thisimage display device.

FIG. 2 is a diagram which shows the coordinate system of the two lightsources that define the hologram.

FIG. 3 is a transverse aberration diagram for a concrete example of thefirst working configuration of the present invention, with FIG. 3(a)showing an angle of view of (X, Y)=(0°, +5°), FIG. 3(b) showing an angleof view of (X, Y)=(0°, 0°), and FIG. 3(c) showing an angle of view of(X, Y)=(0°, −5°), and with the left side of each figure showing thetransverse aberration in the direction of the Y axis and the right sideof each figure showing the transverse aberration in the direction of theX axis. Furthermore, the solid lines indicate light with a wavelength of499.59 nm, the broken lines indicate light with a wavelength of 509.59nm, and the one-dot chain lines indicate light with a wavelength of519.2 nm.

FIG. 4 is another transverse aberration diagram for a concrete exampleof the first working configuration of the present invention. FIG. 4(a)shows an angle of view of (X, Y)=(6.75°, +5°), FIG. 4(b) shows an angleof view of (X, Y) (6.75°, 0°), and FIG. 4(c) shows an angle of view of(X, Y)=(6.75°, −5°). The left side of each figure shows the transverseaberration in the direction of the Y axis, and the right side of eachfigure shows the transverse aberration in the direction of the X axis.Furthermore, the solid lines indicate light with a wavelength of 499.59nm, the broken lines indicate light with a wavelength of 509.59 nm, andthe one-dot chain lines indicate light with a wavelength of 519.2 nm.

FIG. 5 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective angles of view in a concreteexample of the first working configuration of the present invention.

FIG. 6 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective pupil coordinates in a concreteexample of the first working configuration of the present invention.

FIG. 7 is a diagram which shows the brightness within the image plane ina concrete example of the first working configuration of the presentinvention.

FIG. 8 is a diagram which shows the brightness within the pupil plane ina concrete example of the first working configuration of the presentinvention.

FIG. 9 is a diagram which shows the construction of an image displaydevice constituting a second working configuration of the presentinvention, and (in schematic terms) the path of the light rays in thisimage display device.

FIG. 10 is a transverse aberration diagram for a concrete example of thesecond working configuration of the present invention, with FIG. 10(a)showing an angle of view of (X, Y)=(0°, +5°), FIG. 10(b) showing anangle of view of (X, Y)=(0°, 0°), and FIG. 10(c) showing an angle ofview of (X, Y)=(0°, −5°), and with the left side of each figure showingthe transverse aberration in the direction of the Y axis and the rightside of each figure showing the transverse aberration in the directionof the X axis. Furthermore, the solid lines indicate light with awavelength of 453.38 nm, the broken lines indicate light with awavelength of 463.38 nm, and the one-dot chain lines indicate light witha wavelength of 443.38 nm.

FIG. 11 is another transverse aberration diagram for a concrete exampleof the second working configuration of the present invention. FIG. 11(a)shows an angle of view of (X, Y)=(6.75°, +5°), FIG. 11(b) shows an angleof view of (X, Y)=(6.75°, 0°), and FIG. 11(c) shows an angle of view of(X, Y)=(6.75°, −5°). The left side of each figure shows the transverseaberration in the direction of the Y axis, and the right side of eachfigure shows the transverse aberration in the direction of the X axis.Furthermore, the solid lines indicate light with a wavelength of 453.38nm, the broken lines indicate light with a wavelength of 463.38 nm, andthe one-dot chain lines indicate light with a wavelength of 443.38 nm.

FIG. 12 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective angles of view in a concreteexample of the second working configuration of the present invention.

FIG. 13 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective pupil coordinates in a concreteexample of the second working configuration of the present invention.

FIG. 14 is a diagram which shows the brightness within the image planein a concrete example of the second working configuration of the presentinvention.

FIG. 15 is a diagram which shows the brightness within the pupil planein a concrete example of the second working configuration of the presentinvention.

FIG. 16 is a diagram which shows the construction of an image displaydevice constituting a third working configuration of the presentinvention, and (in schematic terms) the path of the light rays in thisimage display device.

FIG. 17 is a transverse aberration diagram for a concrete example of thethird working configuration of the present invention, with FIG. 17(a)showing an angle of view of (X, Y)=(0°, +5°), FIG. 17(b) showing anangle of view of (X, Y) (0°, 0°), and FIG. 17(c) showing an angle ofview of (X, Y)=(0°, −5°), and with the left side of each figure showingthe transverse aberration in the direction of the Y axis and the rightside of each figure showing the transverse aberration in the directionof the X axis. Furthermore, the solid lines indicate light with awavelength of 641.16 nm, the broken lines indicate light with awavelength of 651.16 nm, and the one-dot chain lines indicate light witha wavelength of 631.16 nm.

FIG. 18 is another transverse aberration diagram for a concrete exampleof the third working configuration of the present invention. FIG. 18(a)shows an angle of view of (X, Y)=(6.75°, +5°), FIG. 18(b) shows an angleof view of (X, Y)=(6.75°, 0°), and FIG. 18(c) shows an angle of view of(X, Y)=(6.75°, −5°). The left side of each figure shows the transverseaberration in the direction of the Y axis, and the right side of eachfigure shows the transverse aberration in the direction of the X axis.Furthermore, the solid lines indicate light with a wavelength of 641.16nm, the broken lines indicate light with a wavelength of 651.16 nm, andthe one-dot chain lines indicate light with a wavelength of 631.16 nm.

FIG. 19 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective angles of view in a concreteexample of the third working configuration of the present invention.

FIG. 20 is a diagram which shows the relationship between diffractionefficiency and wavelength for respective pupil coordinates in a concreteexample of the third working configuration of the present invention.

FIG. 21 is a diagram which shows the brightness within the image planein a concrete example of the third working configuration of the presentinvention.

FIG. 22 is a diagram which shows the brightness within the pupil planein a concrete example of the third working configuration of the presentinvention.

FIG. 23 is a diagram which shows the brightness within the image planeof an image display device constituting a fourth working configurationof the present invention, for respective colors.

FIG. 24 is a diagram which shows the brightness within the pupil planeof an image display device constituting a fourth working configurationof the present invention, for respective colors.

FIG. 25 is an explanatory diagram of the Bragg condition. FIG. 25(a)shows the state during exposure of the hologram, and FIG. 25(b) showsthe state during use of the hologram.

FIG. 26 is a diagram which shows the relationship of the variation(shift) in the dominant diffraction wavelength to the variation in theangle of incidence on the reflective type hologram optical element.

FIG. 27 is a diagram which shows the wavelength characteristics of theilluminating light source in the image display devices of the firstthrough fourth working configurations of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Image combiners and image display devices constituting workingconfigurations of the present invention will be described below withreference to the figures.

[First Working Configuration]

FIG. 1 is a diagram which shows the construction of an image displaydevice constituting a first working configuration of the presentinvention, and (in schematic terms) the path of the light rays (only thelight rays from the image display element 2) in this image displaydevice.

Here, an X axis, a Y axis and a Z axis that are mutually perpendicularare defined as shown in FIG. 1. Specifically, the left-right directionin the plane of the page in FIG. 1 is taken as the Z axis, and thedirection in which the Z coordinate value increases is defined as“right.” The vertical direction in the plane of the page in FIG. 1 istaken as the Y axis, and the direction in which the Y coordinate valueincreases is defined as “up.” The direction perpendicular to the planeof the page in FIG. 1 is taken as the X axis, and the system is aright-handed system, i.e., the inward direction from the plane of thepage in FIG. 1 is defined as the direction in which the X coordinatevalue increases. Furthermore, the Y-axis direction may also be caused tocoincide with the actual vertical direction, or may be some otherappropriate direction. These definitions are also the same for FIGS. 9and 16 described later.

The image display device constituting the present working configurationcomprises an image combiner 1 and an image display element 2.

In the present working configuration, a transmitting type LCD is used asthe image display element 2. The image display element 2 is illuminatedfrom the back with light source light from a light source consisting ofan LED 3 and a reflective mirror 4 such as a parabolic mirror. The lightsource light is subjected to spatial light modulation, and lightindicating the display image is transmitted. Furthermore, it goeswithout saying that it would also be possible to use some other elementsuch as a reflective type LCD, or to use an electroluminescent lightemitting element, as the image display element 2.

In the present working configuration, a three-color LED is used as theLED 3. FIG. 27 shows the emission spectrum of the LED 3. In FIG. 27, theline LR indicates the emission spectrum of the red light emitting partof the LED 3, the line LG indicates the emission spectrum of the greenlight emitting part of the LED 3, and the line LB indicates the emissionspectrum of the blue light emitting part of the LED 3. As is seen fromFIG. 27, the light emitted by the LED 3 has respective peak wavelengthsin the R (red) wavelength region, G (green) wavelength region and B(blue) wavelength region, and has respective intensities in therespective wavelength regions extending before and after the respectivepeak wavelengths. The full width at half maximum FWHMr of the spectralintensity for the peak wavelength in the R wavelength region of this LED3 is 23 nm, the full width at half maximum FWHMg for the peak wavelengthin the G wavelength region is 60.8 nm, and the full width at halfmaximum FWHMb for the peak wavelength in the B wavelength region is 29nm. These points are also the same in the respective workingconfigurations described later.

Furthermore, in the present working configuration, the device isconstructed so that the reflective type HOE 6 selectively diffracts andreflects only the G wavelength band component; accordingly, asingle-color LED for G which emits only the G wavelength regioncomponent in FIG. 27 may also be used as the LED 3.

The image combiner 1 comprises a plate-form part 5 which is constructedin the form of parallel flat plates with the upper portions removed froman optical material such as glass or plastic. Of course, the plate-formpart 5 may also have (for example) an optical power that is used tocorrect the visual acuity of the user. In this case, for example, atleast one surface of the two surfaces 5 a and 5 b of the plate-form part5 in the direction of the Z axis is constructed as a curved surface.These points are also the same in the respective working configurationsdescribed later. Furthermore, in the present working configuration, theupper portion of the plate-form part 5 protrudes to the right in thefigure, and the upper surface 5 c of this upper portion is formed as ananamorphic non-spherical surface. Moreover, the plate-form part 5 alsoextends downward in FIG. 1; however, this is omitted from the figure.

The plate-form part 5 is mounted on the head of the user via asupporting member such as a frame (not shown in the figure) in the samemanner as a spectacle lens, and is positioned in front of the eye (notshown in the figure) of the user. In FIG. 1, P indicates an exit pupilfor light from the image display element 2 of the image combiner 1, andPO indicates the center of the exit pupil P. The image combiner 1 ismounted on the user so that this exit pupil P substantially coincideswith the pupil of the eye of the user. In FIG. 1, the Z-axis directioncoincides with the direction of thickness of the plate-form part 5. Theeye-side surface 5 a and opposite-side surface 5 b of the plate-formpart 5 are parallel to the XY plane. Furthermore, although this is notshown in the figure, the LED 3, reflective mirror 4 and image displayelement 2 are also supported by the supporting member mentioned above.As a result, the image display element 2 is disposed in a positionlocated above and to the right of the plate-form part 5 within the planeof the page in the figure, so that the observation of the outside worldby the user is not impeded, and so that the image display element doesnot create any hindrance when the user mounts the image display device.

Of course, it would also be possible to dispose the image displayelement 2 in some other appropriate place, and to conduct the displayimage to the position of the image display element 2 in FIG. 1 by meansof a relay optical system; furthermore, it would also be possible toform an image in this position using a scanning optical system. Thesepoints are also the same in the respective working configurationsdescribed later.

Moreover, in FIG. 1, the points A1 and A2 respectively indicate thepositions of both ends of the display part of the image display element2 within the plane of the page in the figure. Furthermore, the point A0indicates the center of this display part.

The image combiner 1 is constructed so that the light from the imagedisplay element 2 is superimposed on the light (hereafter referred to as“outside world light”) that is transmitted through the plate-form part 5so as to pass through the thickness d of the plate-form part 5 from thefront of the plate-form part 5 (i.e., so as to be incident from thesurface 5 b and emitted from the surface 5 a), and is then conducted tothe eye of the user.

In the present working configuration, a reflective type hologram opticalelement (reflective type HOE) 6 is disposed inside the plate-form part 5in the vicinity of the position that faces the eye of the user in theplate-form part 5. In the present working configuration, the reflectivetype HOE 6 is inclined at a specified angle with respect to the surfaces5 a and 5 b as shown in FIG. 1.

For example, the reflective type HOE 6 can be manufactured by beingbonded to a small piece of the same material as that of the plate-formpart 5; then, this small piece can be placed in the mold frame thatforms the plate-form part 5, and the reflective type HOE 6 can beinstalled inside the plate-form part 5 by pouring the material of theplate-form part 5 in a molten state into the mold frame, and thensolidifying this material.

In the present working configuration, the reflective type HOE 6selectively reflects only the light of the component contained in the Gwavelength band shown in FIG. 27 (among the light from the image displayelement 2). On the other hand, the reflective type HOE 6 transmits thelight of almost all wavelength regions of the outside world light (notshown in the figures) without deflecting this light. Furthermore, it isdesirable that an HOE with high wavelength selectivity be used as thereflective type HOE 6 so that interference with the outside world lightis minimized.

As is shown in FIG. 1, the reflective type HOE 6 has characteristicsthat selectively reflect only light of the component contained in the Gwavelength band shown in FIG. 27 (among the light from the image displayelement 2) toward the pupil of the observer, and also has an opticalpower so that this HOE has a specified image focusing action. Thereflective type HOE 6 may have a flat surface, or may have a curvedsurface. In cases where an HOE with a curved surface is used as thereflective type HOE 6, if the center of curvature of the curved surfaceis disposed on the side of the eye of the user, then the amount ofaberration fluctuation according to the angle of view that is generatedby the reflective type HOE 6 when the angle of view is large is reduced,which is desirable.

For example, photo-polymers, photo-resists, photochromic materials,photodichromic materials, silver salt emulsions, gelatin bichromate,gelatin dichromate, plastics, ferroelectric materials, magnetic opticalmaterials, electro-optical materials, amorphous semiconductors,photo-refractive materials, and the like can be used as the hologramphotosensitive material that is used to construct the reflective typeHOE 6. Furthermore, the reflective type HOE 6 can be manufactured bysimultaneously illuminating such a material with light from two lightsources using an optical system that is used for such manufactureaccording to publicly known methods.

The light that passes through an arbitrary point on the display part ofthe image display element 2 enters the interior of the plate-form part 5from the upper surface 5 c of the upper part of the plate-form part 5,and is then incident on the region R1 of the surface 5 a of theplate-form part 5 at an angle of incidence that is greater than thecritical angle, so that this light is totally reflected by the regionR1. This light is then incident on the region R2 of the surface 5 b ofthe plate-form part 5 at an angle of incidence that is greater than thecritical angle, so that this light is totally reflected by the regionR2. Furthermore, this light is then incident on the region R3 of thesurface 5 a of the plate-form part 5 at an angle of incidence that isgreater than the critical angle, so that the light is totally reflectedby the region R3. Then, the light is incident on the reflective type HOE6. In this case, this light is subjected to a reflective and diffractiveeffect that has wavelength selectivity (G light selectivity in thepresent working configuration), and an image focusing effect, by thereflective type HOE 6. Subsequently, this light is emitted to theoutside of the plate-form part 5 from the region R4 of the surface 5 aof the plate-form part 5. In this case, the light leaving the samelocation on the image display element 2 is incident on the pupil of theeye of the user, which is placed on the exit pupil P so that an enlargedfalse image is formed at a specified distance from the exit pupil P (1 min the case of the present working configuration; this distance is alsothe same in the other working configurations described later, and mayalso be set, for example, at infinity).

The light that reaches the eye of the user after being emitted from theimage display element 2 and diffracted and reflected by the reflectivetype HOE 6 has only a G light component in accordance with the emissionspectrum characteristics of the LED 3 and the wavelength selectivity ofthe reflective type HOE 6. Here, the light rays that are emitted from anarbitrary point on the image display element 2 and that reach the centerP0 of the exit pupil P (among the G light that reaches the eye of theuser after being emitted from the image display element 2 and diffractedand reflected by the reflective type HOE (i.e., the light of the Gwavelength region in FIG. 27)) are called the chief rays with respect tothe G wavelength region.

In the present working configuration, if the wavelength at which thediffraction efficiency shows a maximum value when the chief rays withrespect to the G wavelength region that are emitted from the center ofthe display part of the image display element 2 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(og), and ifthe wavelength at which the diffraction efficiency shows a maximum valuewhen the chief rays with respect to the G wavelength region that areemitted from the peripheral portions of the display part of the imagedisplay element 2 in the Y direction in FIG. 1 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(yg), theneither Equation (10) or Equation (11) shown below is satisfied.Accordingly, in the present working configuration, as will be understoodfrom the content already described, the image quality in cases where thecenter of the pupil of the eye of the user deviates from the center ofthe exit pupil of the image combiner can be improved.1.013<λ_(yg)/λ_(og)  (10)λ_(yg)/λ_(og)<0.98  (11)

Furthermore, in the present working configuration, Equation (12) shownbelow is satisfied. Accordingly, in the present working configuration,as will be understood from the content already described, the amount ofthe wavelength shift caused by the angle of view with respect to the Gwavelength region width of the emission spectrum of the LED 3 issuppressed, so that the danger that a drop in the amount of light willoccur in portions of the screen is eliminated.0.2<|(λ_(yg)−λ_(og))/FWHMg|  (12)

Furthermore, in the present working configuration, if the angle ofincidence (angle calculated in air) on the center of the reflective typeHOE 6 from the light source located on the side of the eye of theobserver during playback (of the two light sources used to expose thereflective type HOE 6 (corresponding the G wavelength region) duringmanufacture) is designated as θ1 g, and if the angle of reflection(angle calculated in air) at the reflective type hologram opticalelement of the light rays that are emitted from the center of thedisplay part of the image display element 2 and that are directed towardthe center P0 of the exit pupil P is designated as θ2, then Equation(13) shown below is satisfied. Accordingly, in the present workingconfiguration, as will be understood from the content already described,the reduction in light at the ends of the angle of view can be balancedin a state that is close to the center distribution.0.8°<|θ1 g−θ2|  (13)

Here, a concrete example of the first working configuration will bedescribed with reference to FIG. 1. In the design of this concreteexample, Code V (commercial name) manufactured by the U.S. firm ofOptical Research Associates, which is well known in this technicalfield, was used as the design program. In this case, the path of thelight rays emitted from the center A0 of the display part of the imagedisplay element 2 and passing through the center P0 of the exit pupil Pis defined as the optical axis of this optical device as a whole. Inthis concrete example, the optical axis is not a single straight line,but rather has a shape in which mutually inclined line segments areconnected. These points are also the same in the concrete examples ofrespective working configurations described later.

The various optical quantities of this concrete example are as describedbelow.

The diameter of the exit pupil P is 3 mm. The visual field angle in theupward direction within the plane of the page in the figure is 5°. Thevisual field angle in the downward direction within the plane of thepage in the figure is −5°. The visual field angle in the direction ofdepth of the page is +6.75°. The screen size in the plane of the page inthe figure (i.e., the length between the point A1 and the point A2) is3.6 mm. The screen size in the direction of depth of the page is 4.8 mm.The thickness d of the plate-form part 5 is 3.5 mm. The wavelength usedis the wavelength width from approximately 480 nm to approximately 540nm. The refractive index nd of the plate-form part 5 with respect to awavelength of 587.56 nm (d line) is 1.596229, and the Abbe number vd is40.4.

With regard to the definition of the HOE 6, the hologram is definitivelydefined by defining the two light beams that are used for exposure. Thetwo light beams are defined by the positions of the respective lightsources and either the convergence (VIR) or divergence (REA) of thebeams emitted from the respective light sources. The coordinates of thefirst point light source (HV1) are designated as (HX1, HY1, HZ1), andthe coordinates of the second point light source are designated as (HX2,HY2, HZ2). In the case of these coordinates, as is shown in FIG. 2, thepoint of intersection between the HOE plane and the optical axis istaken as the origin, the Z axis is taken in the direction of the opticalaxis, the upward direction in the plane of the page within the HOE planeis taken as the Y axis, and the direction of depth of the page is takenas the X axis, so that these coordinates are different from thecoordinates defined in connection with FIG. 1.

Furthermore, an emulsion with a thickness of 20 μm, a refractive indexof 1.493 and a refractive index modulation of 0.03 is used as theemulsion that records the hologram. The exposure wavelength is 532 nm,and it is assumed that the shrinkage rate of the emulsion is 3.3%. Sincethe fluctuation in the wavelength of the playback light caused byshrinkage is in a proportional relationship, the wavelength is alsoshortened by 3.3%, so that the center wavelength during playback is 512nm. The plane of the HOE 6 is a plane whose center is located 1.7 mm tothe right along the Z axis in FIG. 1 from the surface 5 a, and whoseorientation is rotated 30° in the clockwise direction on the plane ofthe page from the same direction as the Y axis. The HOE 6 has a phasefunction component in order to optimize the image focusing performance.

To describe the phase function here, the phase function is a functionthat defines the amount of non-spherical phase conversion other thanthat defined by the two pure point light sources of the HOE 6; in theoptical design program Code V, this can be designated using polynomialcoefficients of the X- and Y-axis components or the like.

Furthermore, the various quantities used for ray tracing in thisconcrete example are shown in Table 2 below. The order of the opticalplanes (order of the plane numbers) runs from the plane of the pupil ofthe eye of the user (=plane of the exit pupil P of the image combiner 1)to the image display element 2. Furthermore, in Table 2, the referencesymbols in FIG. 1 corresponding to the respective plane numbers areindicated as “symbols” in parentheses. This point is also the same intables described later. TABLE 2 Plane number (symbol) Curvature radiusMedium nd νd 1 (P) INFINITY 2 (5a:R4) INFINITY 1.596229 40.4 3 (6)INFINITY 1.596229 40.4 Reflective plane Hologram plane: Definition oftwo light beams HV1: VIR HV2: VIR HX1: 0.000000 × 10⁺⁰⁰ HY1: 0.214385 ×10⁺⁰⁸ HZ1: 0.155769 × 10⁺⁰⁸ HX2: 0.000000 × 10⁺⁰⁰ HY2: 0.181933 × 10⁺⁰⁶HZ2: −.516363 × 10⁺⁰⁶ Phase coefficient C2: 4.7919 × 10⁻⁰¹ C3: −1.5313 ×10⁻⁰²   C5: −8.5586 × 10⁻⁰³   C7:  4.4199 × 10⁻⁰⁴ C9: 3.8390 × 10⁻⁰⁴C10: 5.6408 × 10⁻⁰⁶ C12: 1.2235 × 10⁻⁰⁴ C14: 4.7278 × 10⁻⁰⁵ C16: −1.3514× 10⁻⁰⁵   C18:  3.5083 × 1O⁻⁰⁵ C20: 9.7776 × 10⁻⁰⁶ C21: 3.5859 × 10⁻⁰⁷C23: −3.8342 × 10⁻⁰⁶   C25: −7.3404 × 10⁻⁰⁷   C27: −3.3707 × 10⁻⁰⁶  C29: 7.5311 × 10⁻⁰⁷ C31: −3.7364 × 10⁻⁰⁶   C33: −2.6324 × 10⁻⁰⁶   C35:−1.0178 × 10⁻⁰⁶   C36: 6.7531 × 10⁻⁰⁸ C38: 4.8718 × 10⁻⁰⁷ C40:  3.5228 ×10⁻⁰⁷ C42: 3.1571 × 10⁻⁰⁸ C44: 3.5833 × 10⁻⁰⁷ C46: −2.8708 × 10⁻⁰⁹  C48: 1.8285 × 10⁻⁰⁷ C50:  2.1392 × 10 ⁰⁷  C52: 8.7363 × 10⁻⁰⁸ C54:4.4404 × 10⁻⁰⁸ C55: 5.1216 × 10⁻¹⁰ C57: −5.0692 × 10⁻⁰⁹   C59: −2.8768 ×10⁻⁰⁸   C61: −1.8789 × 10⁻⁰⁸   C63: 6.2577 × 10⁻⁰⁹ C65: −1.4146 ×10⁻⁰⁸   4 (5a:R3) INFINITY 1.596229 40.4 Reflective plane 5 (5b:R2)INFINITY 1.596229 40.4 Reflective plane 6 (5a:R1) INFINITY 1.596229 40.4Reflective plane 7 (5c) −40.57208 Anamorphic non−spherical surface KY:0.000000 KX: 0.000000 Curvature radius in X direction: −20.63634 AR:0.979301 × 10⁻⁰⁵ BR: −.785589 × 10⁻⁰⁶ CR: −.561534 × 10⁻⁰⁸ DR: 0.690209× 10 ³⁸ AP: −.245366 × 10⁺⁰¹ BP: −.272167 × 10⁺⁰⁰ CP: −.123202 × 10⁺⁰¹DP: 0.211276 × 10⁺⁰⁶ 8 (2) INFINITY

The definition of the phase function used in Table 2 expresses theoptical path difference to which the light rays incident on a pointdesignating the HOE as a position on the XY coordinate plane aresubjected as a value that is normalized by the wavelength used; if m andn are assumed to be integers, then this is determined by designatingpolynomial coefficients expressed by Equation (14) in general form shownbelow. Up to 65 such coefficients can be designated; in order, these arecalled C1, C2, C3, . . . , C65, and when the order of the coefficientsis expressed by integers j, then a correspondence is established so thatthe relationship expressed by Equation (15) shown below holds truebetween the integers m and n that indicate the order numbers of the Xcoordinates and Y coordinates. Specifically, in the present example, thephase function is defined by the polynomial equation of Equation (16)shown below. Such a definition of the phase function is also the samefor tables described later. $\begin{matrix}{{\sum\limits_{m = 0}^{10}\quad{\sum\limits_{n = 0}^{10}\quad{{CmnX}^{m}Y^{n}}}},{{{where}\quad{Cmn}} = 0}} & (14) \\{j = \frac{\left( {m + n} \right)^{2} + m + {3n}}{2}} & (15) \\{{C1X} + {C2Y} + {C3X}^{2} + {c4XY} + \ldots + {C65Y}^{10}} & (16)\end{matrix}$

With regard to the definition of the anamorphic non-spherical surface 5c used here, this can be defined by expressing the Z-axis coordinatevalue of a point (x, y) on the curved surface 5 c where the optical axisof the curved surface 5 c is taken as the Z coordinate axis (i.e., theamount of sag) as shown in Equation (17) below. $\begin{matrix}{\frac{{CUXx}^{2} + {CUYy}^{2}}{1 + \sqrt{1 - {\left( {1 + {KX}} \right){CUX}^{2}x^{2}} - {\left( {1 + {KY}} \right){CUY}^{2}y^{2}}}} +} & (17) \\{{{AR}\left\{ {{\left( {1 - {AP}} \right)x^{2}} + {\left( {1 + {AP}} \right)y^{2}}} \right\}^{2}} +} & \quad \\{{{BR}\left\{ {{\left( {1 - {BP}} \right)x^{2}} + {\left( {1 + {BP}} \right)y^{2}}} \right\}^{3}} +} & \quad \\{{{CR}\left\{ {{\left( {1 - {CP}} \right)x^{2}} + {\left( {1 + {CP}} \right)y^{2}}} \right\}^{4}} +} & \quad \\{{DR}\left\{ {{\left( {1 - {DP}} \right)x^{2}} + {\left( {1 + {DP}} \right)y^{2}}} \right\}^{5}} & \quad\end{matrix}$

In Equation (17), CUX indicates the curvature radius in the X-axisdirection, CUY indicates the curvature radius in the Y-axis direction,KX is a conical constant in the X-axis direction, KY is a conicalconstant in the Y-axis direction, AR is a fourth-order non-sphericalcoefficient that is rotationally symmetrical about the Z axis, BR is asixth-order non-spherical coefficient that is rotationally symmetricalabout the Z axis, CR is an eighth-order non-spherical coefficient thatis rotationally symmetrical about the Z axis, DR is a tenth-ordernon-spherical coefficient that is rotationally symmetrical about the Zaxis, AP is a rotationally asymmetrical fourth-order non-sphericalcoefficient, BP is a rotationally asymmetrical sixth-order non-sphericalcoefficient, CP is a rotationally asymmetrical eighth-ordernon-spherical coefficient, and DP is a rotationally asymmetricaltenth-order non-spherical coefficient.

Furthermore, with regard to the positional relationship of therespective optical planes in the present concrete example, the absolutepositions of the centers of the respective optical planes with thecenter P0 of the first plane (plane No. 1=symbol P in FIG. 1) taken asthe origin (X, Y, Z)=(0, 0, 0), and the amounts of rotation of theseplanes about the X axis (values measured with the counterclockwisedirection taken as the positive direction), are shown in Table 3 below.TABLE 3 X Y Z Rotational angle Plane No. coordinate coordinatecoordinate about X axis (symbol) value value value [degree] 1 (P)0.00000 0.00000 0.00000 0.0000 2 (5a:R4) 0.00000 0.00000 13.00000 0.00003 (6) 0.00000 0.00000 14.70000 −30.0000 4 (5a:R3) 0.00000 0.0000013.00000 0.0000 5 (5b:R2) 0.00000 0.00000 16.50000 0.0000 6 (5a:R1)0.00000 0.00000 13.00000 0.0000 7 (5c) 0.00000 22.80000 13.10522 93.16938 (2) 0.00000 29.16123 24.93254 45.4349

With regard to the position of the first light source of the HOE 6 inthis concrete example, it is seen from

HX1: 0, HY1: 0.214385×10⁺⁰⁸, HZ1: 0.155769×10⁺⁰⁸

that this is the first quadrant of yz coordinates in FIG. 2, that thedistance from the origin is 2.65×10⁷ mm, and that the angle measuredfrom the negative direction of the Z axis is 54 degrees. However, sinceHV1 is VIR, this is convergent light, and is actually incident from theopposite direction. Furthermore, since the two light sources of the HOE6 are defined in air, the distances and angles are corrected for therefractive index and compared in cases where the HOE 6 during playbackis in a medium.

In the case of this example, since the distances are substantiallyinfinite, no conversion is necessary. Since the distance of this lightsource is a distance that is close to the false image between theplayback false image and the exit pupil, the dominant diffractionwavelength is constant at respective positions within the exit pupil.Instead, the dominant diffraction wavelength shifts according to theangle of view.

Meanwhile, with regard to the angles, the angle of incidence of thefirst light source with respect to the normal of the HOE is 54° in air.Here, since the light on the optical axis during playback is incident atan angle of incidence of 30° through a medium with a refractive index ofapproximately 1.6, this angle is 53.1° when calculated in air.Accordingly, the angle of incidence θ1 g of the exposure light on theHOE 6 and the angle of incidence θ2 of the playback light on the HOE 6are shifted by 0.9°. As a result, the dominant diffraction wavelength atan angle of view of 0° is slightly shifted from the playback centerwavelength of 512 nm which takes only shrinkage into account, so thatthis wavelength approaches the peak wavelength of 516 nm of the greenemission spectrum of the light source.

When the diffraction efficiency is calculated for the present concreteexample, the dominant wavelengths of the diffraction efficiency of thelight rays passing through the respective pupil coordinates Py of −1.5mm, 0 mm and +1.5 mm at the respective angles of view of −5°, 0° and +5°(angles of view in the Y direction; the angle of view in the X directionis 0°) are as shown in Table 4 below. Here, the pupil coordinate Py isthe positional coordinate in the direction of the Y axis within the exitpupil P in the plane of the page in FIG. 1; the position of Py=0 mmindicates the center P0 of the exit pupil P. Furthermore, in the case ofthe light rays passing through the pupil coordinate of Py=0 mm, thelight rays at all angles of view are chief rays. TABLE 4 Angle of viewPupil coordinate Py −5° 0° +5° −1.5 mm 529.2 nm 516.04 nm 499.56 nm 0 mm529.2 nm 516.04 nm 499.56 nm +1.5 mm 529.2 nm 516.04 nm 499.56 nm

Furthermore, transverse aberration diagrams used to express the imagefocusing performance of the optical system of the present concreteexample are shown in FIGS. 3 and 4. In FIGS. 3 and 4, transverseaberration diagrams for light rays of the dominant diffractionwavelength±10 nm are shown simultaneously in one diagram for each angleof view. It is seen from FIGS. 3 and 4 that there is little chromaticaberration throughout the entire region within the angle of view, sothat the image focusing performance is superior.

Furthermore, the wavelength characteristics of the diffractionefficiency of the HOE 6 of the present concrete example (characteristicsfor green light) are shown in FIGS. 5 and 6. FIG. 5 shows the wavelengthcharacteristics of the diffraction efficiency of the chief rays (Py=0mm) at respective angles of view of −5°, 0° and +5° (angles of view inthe Y direction; the angle of view in the X direction is 0°). FIG. 6shows the wavelength characteristics of the diffraction efficiency ofthe light rays passing through the respective pupil coordinates of −1.5mm, 0 mm and +1.5 mm at an angle of view of (X, Y)=(0°, 0°). In FIG. 6,the wavelength characteristics for the respective pupil coordinatescoincide and overlap. In FIG. 5, it is shown how the dominantdiffraction wavelength shifts according to the angle of view, while inFIG. 6, it is shown how the dominant diffraction wavelength is notshifted according to the pupil coordinates.

In FIGS. 5 and 6, the emission spectra of the corresponding G wavelengthregions (among the respective wavelength regions of the LED 3 shown inFIG. 27) are also superimposed. In actuality, the quantity of light thatreaches the eye of the observer (i.e., the brightness) is a product ofthese two types of graphs (i.e., a product of the diffraction efficiencyand the emission spectrum of the G wavelength region). The brightnessdistribution within the screen is shown in FIG. 7, and the brightnessdistribution within the pupil plane is shown in FIG. 8. The respectiveplotted points in FIG. 7 correspond to the product of the peaks of thediffraction efficiency at the respective angles of view in FIG. 5 andthe intensity of the light emitted from the LED 3 at the correspondingpeak wavelengths. The respective plotted points in FIG. 8 correspond tothe product of the peaks of the diffraction efficiency at the respectivepupil coordinates in FIG. 6 and the intensity of the light emitted fromthe LED 3 at the corresponding peak wavelengths. Furthermore, thevertical axes in FIGS. 7 and 8 indicate the brightness, which isnormalized with the maximum brightness taken as 1.

In the present concrete example, the respective ratios λ_(yg)/λ_(og) ofthe dominant diffraction wavelength λ_(yg) at angles of view of −50 and+5° to the dominant diffraction wavelength λ_(og) at the center of theangle of view are 1.026 and 0.968, and are thus less than 0.98 andgreater than 1.013, so that the conditions of Equation (10) and Equation(11) described above are satisfied. As a result, the intensity withinthe pupil plane is flat as shown in FIG. 8.

Furthermore, the differences |λ_(yg)−λ_(og)| between the dominantdiffraction wavelengths in the center and periphery of the angle of vieware 13.16 and 16.48, respectively, and the full width at half maximumFWHMg of the light source used in the present concrete example is 60.8nm; accordingly, when the value of the right side of Equation (12) iscalculated, respective values of 0.22 and 0.27 are obtained at angles ofview of −5° and +5°, so that the conditions of Equation (12) aresatisfied. As a result, a balanced brightness is obtained both withinthe pupil plane and within the screen, as is shown in FIGS. 7 and 8.

Furthermore, the difference between the angle θ1 g of the referencelight source and the angle of incidence θ2 of the optical axis of theray tracing is 0.9°, so that the conditions of Equation (13) aresatisfied.

[Second Working Configuration]

FIG. 9 is a diagram which shows the construction of an image displaydevice constituting a second working configuration of the presentinvention, and the path of the light rays (only the light rays from theimage display element 2) in this image display device. In FIG. 9,elements that are the same as elements in FIG. 1, or that correspond toelements in FIG. 1, are labeled with the same symbols, and a redundantdescription is omitted. Furthermore, the LED 3 and reflective mirror 4that constitute the light source are omitted from FIG. 9.

The basic difference between the present working configuration and thefirst working configuration described above is as follows: namely, inthe first working configuration described above, the device wasconstructed so that the reflective type HOE 6 selectively diffracts andreflects only the G wavelength band component, while in the presentworking configuration, the device is constructed so that the reflectivetype HOE 6 selectively diffracts and reflects only the B wavelength bandcomponent.

Furthermore, in the present working configuration, since the device isconstructed so that the reflective type HOE 6 selectively diffracts andreflects only the B wavelength band component, a B single-color LEDwhich emits only the B wavelength region component in FIG. 27 may beused as the LED 3.

Here, the light rays that are emitted from an arbitrary point on theimage display element 2 and that reach the center P0 of the exit pupil P(among the B light that reaches the eye of the user after being emittedfrom the image display element 2 and diffracted and reflected by thereflective type HOE 6 (i.e., the light of the B wavelength region inFIG. 27)) are called the chief rays with respect to the B wavelengthregion.

In the present working configuration, if the wavelength at which thediffraction efficiency shows a maximum value when the chief rays withrespect to the B wavelength region that are emitted from the center ofthe display part of the image display element 2 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(ob), and ifthe wavelength at which the diffraction efficiency shows a maximum valuewhen the chief rays with respect to the B wavelength region that areemitted from the peripheral portions of the display part of the imagedisplay element 2 in the Y direction in FIG. 9 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(yb), theneither Equation (18) or Equation (19) shown below is satisfied.Accordingly, in the present working configuration, as will be understoodfrom the content already described, the image quality in cases where thecenter of the pupil of the eye of the user deviates from the center ofthe exit pupil of the image combiner can be improved.1.013<λ_(yb)/λ_(ob)  (18)λ_(yb)/λ_(ob)<0.98  (19)

Furthermore, in the present working configuration, Equation (20) shownbelow is satisfied. Accordingly, in the present working configuration,as will be understood from the content already described, the amount ofthe wavelength shift caused by the angle of view with respect to the Bwavelength region width of the emission spectrum of the LED 3 issuppressed, so that the danger that a drop in the amount of light willoccur in portions of the screen is eliminated.0.2<|(λ_(yb)−λ_(ob))/FWHMb|  (20)

Furthermore, in the present working configuration, if the angle ofincidence (angle calculated in air) on the center of the reflective typeHOE 6 from the light source located on the side of the eye of theobserver during playback (of the two light sources used to expose thereflective type HOE 6 (corresponding the B wavelength region) duringmanufacture) is designated as θ1 b, and if the angle of reflection(angle calculated in air) at the reflective type hologram opticalelement of the light rays that are emitted from the center of thedisplay part of the image display element 2 and that are directed towardthe center P0 of the exit pupil P is designated as θ2, then Equation(21) shown below is satisfied. Accordingly, in the present workingconfiguration, as will be understood from the content already described,the reduction in light at the ends of the angle of view can be balancedin a state that is close to the center distribution.0.8°<|θ1 b−θ2|  (21)

Here, a concrete example of the present working configuration will bedescribed with reference to FIG. 9. The various optical quantities ofthis concrete example are as described below.

In the present concrete example, the exposure wavelength of the HOE 6 isset at 476 nm. The diameter of the exit pupil P is 3 mm. The visualfield angle in the upward direction within the plane of the page in thefigure is 5°. The visual field angle in the downward direction withinthe plane of the page in the figure is −5°. The visual field angle inthe direction of depth of the page is ±6.75°. The screen size in theplane of the page in the figure (i.e., the length between the point A1and the point A2) is 3.6 mm. The screen size in the direction of depthof the page is 4.8 mm. The thickness d of the plate-form part 5 is 3.5mm. The plate-form part 5 uses the same material as in the concreteexample of the first working configuration described above.

Furthermore, the various quantities used for ray tracing in thisconcrete example are shown in Table 5 below. The order of the opticalplanes (order of the plane numbers) runs from the plane of the pupil ofthe eye of the user (=plane of the exit pupil P of the image combiner 1)to the image display element 2. TABLE 5 Plane number (symbol) Curvatureradius Medium nd νd 1 (P) INFINITY 2 (5a:R4) INFINITY 1.596229 40.4 3(6) INFINITY 1.596229 40.4 Reflective plane Hologram plane: Definitionof two light beams HV1: REA HV2: VIR HX1: 0.000000 × 10⁺⁰⁰ HY1: −.243820× 10⁺⁰² HZ1: −.165512 × 10⁺⁰² HX2: 0.000000 × 10⁺⁰⁰ HY2: −.605332 ×10⁺⁰² HZ2: −.289129 × 10⁺⁰² Phase coefficient C2: 1.7337 × 10⁺⁰⁰ C3:9.2796 × 10⁻⁰³ C5: −1.5977 × 10⁻⁰³ C7: −7.1335 × 10⁻⁰⁵   C9: 2.8492 ×10⁻⁰⁴ CIO: −9.2646 × 10⁻⁰⁶ C12: 1.2395 × 10⁻⁰⁴ C14: 5.5187 × 10⁻⁰⁵ C16:−2.4261 × 10⁻⁰⁵ C18: 1.0132 × 10⁻⁰⁵ C20: −1.2885 × 10⁻⁰⁶   C21:   1.7830× 10⁻⁰⁶ C23: 2.2457 × 10⁻⁰⁶ C25: 5.7068 × 10⁻⁰⁷ C27: −4.5205 × 10⁻⁰⁶C29: 1.7885 × 10⁻⁰⁶ C31: 2.7316 × 10⁻⁰⁷ C33:   3.8019 × 10⁻⁰⁷ C35:−3.3623 × 10⁻⁰⁸   C36: 1.7243 × 10⁻⁰⁸ C38: −3.1054 × 10⁻⁰⁷ C40: −4.3523× 10⁻⁰⁷   C42: −1.3783 × 10⁻⁰⁸   C44:   4.5950 × 10⁻⁰⁷ C46: −2.8238 ×10⁻⁰⁸   C48: −1.5580 × 10⁻⁰⁸   C50: −1.0661 × 10⁻⁰⁸ C52: −2.8648 ×10⁻⁰⁸   C54: 1.1788 × 10⁻⁰⁸ C55: −2.6416 × 10⁻¹⁰ C57: 2.5009 × 10⁻⁰⁸C59: 2.8852 × 10⁻⁰⁸ C61:   1.2417 × 10⁻⁰⁸ C63: 6.2577 × 10⁻⁰⁹ C65:−1.4146 × 10⁻⁰⁸   4 (5a:R3) INFINITY 1.596229 40.4 Reflective plane 5(5b:R2) INFINITY 1.596229 40.4 Reflective plane 6 (5a:R1) INFINITY1.596229 40.4 Reflective plane 7 (5c) −40.57208 Anamorphic non−sphericalsurface KY: 0.000000 KX: 0.000000 Curvature radius in X direction:−20.63634 AR: 0.979301 × 10⁻⁰⁵ BR: −.785589 × 10⁻⁰⁶ CR: −.561534 × 10⁻⁰⁸DR: 0.690209 × 10⁻³⁸ AP: −.245366 × 10⁺⁰¹ BP: −.272167 × 10⁺⁰⁰ CP:−.123202 × 10⁺⁰¹ DP: 0.211276 × 10⁺⁰⁶ 8 (2) INFINITY

Furthermore, with regard to the positional relationship of therespective optical planes in the present concrete example, the absolutepositions of the centers of the respective optical planes with thecenter of the first plane (plane No. 1=symbol P in FIG. 9) taken as theorigin (X, Y, Z)=(0, 0, 0), and the amounts of rotation of these planesabout the X axis (values measured with the counterclockwise directiontaken as the positive direction), are shown in Table 6 below. TABLE 6 XY Z Rotational angle Plane No. coordinate coordinate coordinate about Xaxis (symbol) value value value [degree] 1 (P) 0.00000 0.00000 0.000000.0000 2 (5a:R4) 0.00000 0.00000 13.00000 0.0000 3 (6) 0.00000 0.0000014.70000 −30.0000 4 (5a:R3) 0.00000 0.00000 13.00000 0.0000 5 (5b:R2)0.00000 0.00000 16.50000 0.0000 6 (5a:R1) 0.00000 0.00000 13.000000.0000 7 (5c) 0.00000 22.80000 13.10522 93.1693 8 (2) 0.00000 29.1612324.93254 45.4349

With regard to the position of the first light source of the HOE 6 inthis concrete example, it is seen from

HX1: 0, HY1: −0.243820×10⁺⁰², HZ1: −0.165512×10⁺⁰²

that this is the third quadrant of yz coordinates in FIG. 2, that thedistance from the origin is 26.469 mm, and that the angle measured fromthe negative direction of the Z axis is 55.8 degrees. Furthermore, sinceHV1 is REA, this is divergent light. Since the two light sources of theHOE 6 are defined in air as in the first working configuration, thedistances and angles are corrected for the refractive index and comparedin cases where the HOE 6 during playback is in a medium.

The plane of the HOE 6 is located at a distance of 14.7 mm from thepupil plane; of this distance, 1.7 mm is located in a medium with arefractive index of approximately 1.6. Accordingly, the lengthcalculated in terms of air is 1.06 mm, so that the distance from the HOE6 to the pupil plane calculated in terms of air is 14.06 mm.Consequently, the light source distance in this example is approximatelytwice the distance of the pupil between the false image and the pupil.

Meanwhile, with regard to the angles, the angle of incidence of thefirst light source with respect to the normal of the HOE 6 is 55.8° inair. Here, since the light on the optical axis during playback isincident at an angle of incidence of 30° through a medium with arefractive index of approximately 1.6, this angle is 53.1° whencalculated in air. Accordingly, the angle of incidence θ1 b of theexposure light on the HOE 6 and the angle of incidence θ2 of theplayback light on the HOE 6 are shifted by 2.7°. As a result, thedominant diffraction wavelength at an angle of view of 0° is shiftedfrom the exposure wavelength of 476 nm to 460.3 nm by the shrinkage ofthe emulsion (assumed to be 3.3%); however, this wavelength is furtherslightly shifted as a result of the angular deviation of the first lightsource, so that this wavelength approaches the peak wavelength of 463 nmof the blue emission spectrum of the light source.

When the diffraction efficiency is calculated for the present concreteexample, the dominant wavelengths of the diffraction efficiency of thelight rays passing through the respective pupil coordinates Py of −1.5mm, 0 mm and +1.5 mm at the respective angles of view of −5°, 0° and +5°(angles of view in the Y direction; the angle of view in the X directionis 0°) are as shown in Table 7 below. Here, the pupil coordinate Py isthe positional coordinate in the direction of the Y axis within the exitpupil P in the plane of the page in FIG. 9; the position of Py=0 mmindicates the center P0 of the exit pupil P. Furthermore, in the case ofthe light rays passing through the pupil coordinate of Py=0 mm, thelight rays at all angles of view are chief rays. TABLE 7 Angle of viewPupil coordinate Py −5° 0° +5° −1.5 mm 486.38 nm 469.88 nm 453.38 nm 0mm 479.78 nm 466.58 nm 450.08 nm +1.5 mm 476.48 nm 459.98 nm 443.48 nm

Furthermore, transverse aberration diagrams used to express the imagefocusing performance of the optical system of the present concreteexample are shown in FIGS. 10 and 11. In FIGS. 10 and 11, transverseaberration diagrams for light rays of the dominant diffractionwavelength±10 nm are shown simultaneously in one diagram for each angleof view. It is seen from FIGS. 10 and 11 that there is little chromaticaberration throughout the entire region within the angle of view, sothat the image focusing performance is superior.

The LED 3 (not shown in FIG. 9) having three wavelength regions used inthe present concrete example is the same as that used in the firstworking configuration, and has the emission spectrum shown in FIG. 27.

Furthermore, the wavelength characteristics of the diffractionefficiency of the HOE 6 of the present concrete example (characteristicsfor blue light) are shown in FIGS. 12 and 13. FIG. 12 shows thewavelength characteristics of the diffraction efficiency of the chiefrays (Py=0 mm) at respective angles of view of −5°, 0° and +5° (anglesof view in the Y direction; the angle of view in the X direction is 0°).FIG. 13 shows the wavelength characteristics of the diffractionefficiency of the light rays passing through the respective pupilcoordinates of −1.5 mm, 0 mm and +1.5 mm at an angle of view of (X,Y)=(0°, 0°). In FIG. 12, it is shown how the dominant diffractionwavelength shifts according to the angle of view, while in FIG. 13, itis shown how the dominant diffraction wavelength shifts according to thepupil coordinates. In this concrete example, since the light source iscloser to the pupil than in the first working configuration, adiffraction wavelength shift within the pupil plane also occurs.

In FIGS. 12 and 13, the emission spectra of the corresponding Bwavelength regions (among the respective wavelength regions of the LED 3shown in FIG. 27) are also superimposed. In actuality, the quantity oflight that reaches the eye of the observer (i.e., the brightness) is aproduct of these two types of graphs (i.e., a product of the diffractionefficiency and the emission spectrum of the B wavelength region). Thebrightness distribution within the screen is shown in FIG. 14, and thebrightness distribution within the pupil plane is shown in FIG. 15. Therespective plotted points in FIG. 14 correspond to the product of thepeaks of the diffraction efficiency at the respective angles of view inFIG. 12 and the intensity of the light emitted from the LED 3 at thecorresponding peak wavelengths. The respective plotted points in FIG. 15correspond to the product of the peaks of the diffraction efficiency atthe respective pupil coordinates in FIG. 13 and the intensity of thelight emitted from the LED 3 at the corresponding peak wavelengths.Furthermore, the vertical axes in FIGS. 14 and 15 indicate thebrightness, which is normalized with the maximum brightness taken as 1.

In the present concrete example, the respective ratios λ_(yb)/λ_(ob) ofthe dominant diffraction wavelength λ_(yb) at angles of view of −5° and+5° to the dominant diffraction wavelength λ_(ob) at the center of theangle of view are 1.028 and 0.965, and are thus less than 0.98 andgreater than 1.013, so that the conditions of Equation (18) and Equation(19) described above are satisfied. As a result, the intensity withinthe pupil plane is close to flat as shown in FIG. 15.

Furthermore, the differences |λ_(yb)−λ_(ob)| between the dominantdiffraction wavelengths in the center and periphery of the angle of vieware 13.2 and 16.5, respectively, and the full width at half maximumFWHMb of the light source used in the present concrete example is 29 nm;accordingly, when the value of the right side of Equation (20) iscalculated, respective values of 0.46 and 0.57 are obtained at angles ofview of −5° and +5°, so that the conditions of Equation (20) aresatisfied. As a result, a balanced brightness is obtained both withinthe pupil plane and within the screen, as is shown in FIGS. 14 and 15.

Furthermore, the difference between the angle θ1 b of the referencelight source and the angle of incidence θ2 of the optical axis of theray tracing is 2.7°, so that the conditions of Equation (21) aresatisfied.

[Third Working Configuration]

FIG. 16 is a diagram which shows the construction of an image displaydevice constituting a third working configuration of the presentinvention, and the path of the light rays (only the light rays from theimage display element 2) in this image display device. In FIG. 16,elements that are the same as elements in FIG. 1, or that correspond toelements in FIG. 1, are labeled with the same symbols, and a redundantdescription is omitted. Furthermore, the LED 3 and reflective mirror 4that constitute the light source are omitted from FIG. 16.

The basic difference between the present working configuration and thefirst working configuration described above is as follows: namely, inthe first working configuration described above, the device wasconstructed so that the reflective type HOE 6 selectively diffracts andreflects only the G wavelength band component, while in the presentworking configuration, the device is constructed so that the reflectivetype HOE 6 selectively diffracts and reflects only the R wavelength bandcomponent.

Furthermore, in the present working configuration, since the device isconstructed so that the reflective type HOE 6 selectively diffracts andreflects only the R wavelength band component, an R single-color LEDwhich emits only the R wavelength region component in FIG. 27 may beused as the LED 3.

Here, the light rays that are emitted from an arbitrary point on theimage display element 2 and that reach the center P0 of the exit pupil P(among the R light that reaches the eye of the user after being emittedfrom the image display element 2 and diffracted and reflected by thereflective type HOE 6 (i.e., the light of the R wavelength region inFIG. 27)) are called the chief rays with respect to the R wavelengthregion.

In the present working configuration, if the wavelength at which thediffraction efficiency shows a maximum value when the chief rays withrespect to the R wavelength region that are emitted from the center ofthe display part of the image display element 2 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(or), and ifthe wavelength at which the diffraction efficiency shows a maximum valuewhen the chief rays with respect to the R wavelength region that areemitted from the peripheral portions of the display part of the imagedisplay element 2 in the Y direction in FIG. 16 are diffracted andreflected by the reflective type HOE 6 is designated as λ_(yr), theneither Equation (22) or Equation (23) shown below is satisfied.Accordingly, in the present working configuration, as will be understoodfrom the content already described, the image quality in cases where thecenter of the pupil of the eye of the user deviates from the center ofthe exit pupil of the image combiner can be improved.1.013<λ_(yr)/λ_(or)  (22)λ_(yr)/λ_(or)<0.98  (23)

Furthermore, in the present working configuration, Equation (24) shownbelow is satisfied. Accordingly, in the present working configuration,as will be understood from the content already described, the amount ofthe wavelength shift caused by the angle of view with respect to the Rwavelength region width of the emission spectrum of the LED 3 issuppressed, so that the danger that a drop in the amount of light willoccur in portions of the screen is eliminated.0.2<|(λ_(yr)−λ_(or))/FWHMr|  (24)

Furthermore, in the present working configuration, if the angle ofincidence (angle calculated in air) on the center of the reflective typeHOE 6 from the light source located on the side of the eye of theobserver during playback (of the two light sources used to expose thereflective type HOE 6 (corresponding the R wavelength region) duringmanufacture) is designated as θ1 r, and if the angle of reflection(angle calculated in air) at the reflective type hologram opticalelement of the light rays that are emitted from the center of thedisplay part of the image display element 2 and that are directed towardthe center P0 of the exit pupil P is designated as θ2, then Equation(25) shown below is satisfied. Accordingly, in the present workingconfiguration, as will be understood from the content already described,the reduction in light at the ends of the angle of view can be balancedin a state that is close to the center distribution.0.8°<|θ1 r−θ2|  (25)

Here, a concrete example of the present working configuration will bedescribed with reference to FIG. 16. The various optical quantities ofthis concrete example are as described below.

In the present concrete example, the exposure wavelength of the HOE 6 isset at 647 nm. The diameter of the exit pupil P is 3 mm. The visualfield angle in the upward direction within the plane of the page in thefigure is 5°. The visual field angle in the downward direction withinthe plane of the page in the figure is −5°. The visual field angle inthe direction of depth of the page is ±6.75°. The screen size in theplane of the page in the figure (i.e., the length between the point A1and the point A2) is 3.6 mm. The screen size in the direction of depthof the page is 4.8 mm. The thickness d of the plate-form part 5 is 3.5mm. The plate-form part 5 uses the same material as in the concreteexample of the first working configuration described above.

Furthermore, the various quantities used for ray tracing in thisconcrete example are shown in Table 8 below. The order of the opticalplanes (order of the plane numbers) runs from the plane of the pupil ofthe eye of the user (=plane of the exit pupil P of the image combiner 1)to the image display element 2. TABLE 8 Plane number (symbol) Curvatureradius Medium nd νd 1 (P) INFINITY 2 (5a:R4) INFINITY 1.596229 40.4 3(6) INFINITY INFINITY 1.596229 40.4 Reflective plane Hologram plane:Definition of two light beams HV1: REA HV2: VIR HX1: 0.000000 × 10⁺⁰⁰HY1: −.124597 × 10⁺⁰² HZ1: −.841764 × 10⁺⁰¹ HX2: 0.000000 × 10⁺⁰⁰ HY2:−.132998 × 10⁺⁰⁶ HZ2: −.516363 × 10⁺⁰⁶ Phase coefficient C2: 1.0778 ×10⁺⁰⁰ C3: 1.8026 × 10⁻⁰² C5: 1.7958 × 10⁻⁰³ C7: −1.3475 × 10⁻⁰³   C9:−1.2758 × 10⁻⁰⁴   C10: −3.8516 × 10⁻⁰⁵   C12: 1.8068 × 10⁻⁰⁴ C14: 7.4199× 10⁻⁰⁵ C16: −1.5243 × 10⁻⁰⁵   C18: 6.8532 × 10⁻⁰⁶ C20: −3.9793 ×10⁻⁰⁶   C21: 1.5435 × 10⁻⁰⁶ C23: 1.4019 × 10⁻⁰⁶ C25: 3.3772 × 10⁻⁰⁷ C27:−4.4250 × 10⁻⁰⁶   C29: 1.5818 × 10⁻⁰⁶ C31: −1.4761 × 10⁻⁰⁷   C33: 4.2293× 10⁻⁰⁷ C35: 3.1500 × 10⁻⁰⁸ C36: 2.4298 × 10⁻⁰⁸ C38: −2.5636 × 10⁻⁰⁷  C40: −3.8160 × 10⁻⁰⁷   C42: −4.2124 × 10⁻⁰⁹   C44: 4.6437 × 10⁻⁰⁷ C46:−2.2460 × 10⁻⁰⁸   C48: −1.0668 × 10⁻⁰⁸   C50: 2.3493 × 10⁻⁰⁸ C52:−3.3721 × 10⁻⁰⁸   C54: 1.1657 × 10⁻⁰⁸ C55: −3.7867 × 10⁻¹⁰   C57: 1.9619× 10⁻⁰⁸ C59: 2.6564 × 10⁻⁰⁸ C61: 7.2079 × 10⁻⁰⁹ C63: 6.8830 × 10⁻⁰⁹ C65:−1.7445 × 10⁻⁰⁸   4 (5a:R3) INFINITY 1.596229 40.4 Reflective plane 5(5b:R2) INFINITY 1.596229 40.4 Reflective plane 6 (5a:R1) INFINITY1.596229 40.4 Reflective plane 7 (5c) −40.57208 Anamorphic non−sphericalsurface KY: 0.000000 KX: 0.000000 Curvature radius in X direction:−20.63634 AR: 0.979301 × 10⁻⁰⁵ BR: −.785589 × 10⁻⁰⁶ CR: −.561534 × 10⁻⁰⁸DR: 0.690209 × 10⁻³⁸ AP:  −.245366 × 10⁺⁰¹    BP: −.272167 × 10⁺⁰⁰ CP:−.123202 × 10⁺⁰¹ DP: 0.211276 × 10⁺⁰⁶ 8 (2) INFINITY

Furthermore, with regard to the positional relationship of therespective optical planes in the present concrete example, the absolutepositions of the centers of the respective optical planes with thecenter of the first plane (plane No. 1=symbol P in FIG. 16) taken as theorigin (X, Y, Z)=(0, 0, 0), and the amounts of rotation of these planesabout the X axis (values measured with the counterclockwise directiontaken as the positive direction), are shown in Table 9 below. TABLE 9 XY Z Rotational angle Plane No. coordinate coordinate coordinate about Xaxis (symbol) value value value [degree] 1 (P) 0.00000 0.00000 0.000000.0000 2 (5a:R4) 0.00000 0.00000 13.00000 0.0000 3 (6) 0.00000 0.0000014.70000 −30.0000 4 (5a:R3) 0.00000 0.00000 13.00000 0.0000 5 (5b:R2)0.00000 0.00000 16.50000 0.0000 6 (5a:R1) 0.00000 0.00000 13.000000.0000 7 (5c) 0.00000 22.80000 13.10522 93.1693 8 (2) 0.00000 29.1612324.93254 45.4349

With regard to the position of the first light source of the HOE 6 inthis concrete example, it is seen from

HX1: 0, HY1: −0.124597×10⁺⁰², HZ1: −0.841764×10⁺⁰¹

that this is the third quadrant of yz coordinates in FIG. 2, that thedistance from the origin is 15.04 mm, and that the angle measured fromthe negative direction of the Z axis is 56 degrees. Furthermore, sinceHV1 is REA, this is divergent light. Since the two light sources of theHOE 6 are defined in air as in the first working configuration, thedistances and angles are corrected for the refractive index and comparedin cases where the HOE 6 during playback is in a medium.

The plane of the HOE 6 is located at a distance of 14.7 mm from thepupil plane; of this distance, 1.7 mm is located in a medium with arefractive index of approximately 1.6. Accordingly, the lengthcalculated in terms of air is 1.06 mm, so that the distance from the HOE6 to the pupil plane calculated in terms of air is 14.06 mm.Consequently, the light source distance in this example is a distancewhich is such that the light source is close to the pupil between thefalse image and the pupil.

Meanwhile, with regard to the angles, the angle of incidence of thefirst light source with respect to the normal of the HOE 6 is 56° inair. Here, since the light on the optical axis during playback isincident at an angle of incidence of 30° through a medium with arefractive index of approximately 1.6, this angle is 53.1° whencalculated in air. Accordingly, the angle of incidence θ1 r of theexposure light on the HOE 6 and the angle of incidence θ2 of theplayback light on the HOE 6 are shifted by 2.9°. As a result, thedominant diffraction wavelength at an angle of view of 0° is shiftedfrom the exposure wavelength of 647 nm to 625.6 nm by the shrinkage ofthe emulsion (assumed to be 3.3%); however, this wavelength is furtherslightly shifted as a result of the angular deviation of the first lightsource.

When the diffraction efficiency is calculated for the present concreteexample, the dominant wavelengths of the diffraction efficiency of thelight rays passing through the respective pupil coordinates Py of −1.5mm, 0 mm and +1.5 mm at the respective angles of view of −5°, 0° and +50(angles of view in the Y direction; the angle of view in the X directionis 0°) are as shown in Table 10 below. Here, the pupil coordinate Py isthe positional coordinate in the direction of the Y axis within the exitpupil P in the plane of the page in FIG. 16; the position of Py=0 mmindicates the center P0 of the exit pupil P. Furthermore, in the case ofthe light rays passing through the pupil coordinate of Py=0 mm, thelight rays at all angles of view are chief rays. TABLE 10 Angle of viewPupil coordinate Py −5° 0° +5° −1.5 mm 654.32 nm 644.45 nm 628.00 nm 0mm 644.45 nm 634.58 nm 621.42 nm +1.5 mm 631.29 nm 621.42 nm 608.26 nm

Furthermore, transverse aberration diagrams used to express the imagefocusing performance of the optical system of the present concreteexample are shown in FIGS. 17 and 18. In FIGS. 17 and 18, transverseaberration diagrams for light rays of the dominant diffractionwavelength±10 nm are shown simultaneously in one diagram for each angleof view. It is seen from FIGS. 17 and 18 that there is little chromaticaberration throughout the entire region within the angle of view, sothat the image focusing performance is superior.

The LED 3 (not shown in FIG. 16) having three wavelength regions used inthe present concrete example is the same as that used in the firstworking configuration, and has the emission spectrum shown in FIG. 27.

Furthermore, the wavelength characteristics of the diffractionefficiency of the HOE 6 of the present concrete example (characteristicsfor red light) are shown in FIGS. 19 and 20. FIG. 19 shows thewavelength characteristics of the diffraction efficiency of the chiefrays (Py=0 mm) at respective angles of view of −5°, 0° and +5° (anglesof view in the Y direction; the angle of view in the X direction is 0°).FIG. 20 shows the wavelength characteristics of the diffractionefficiency of the light rays passing through the respective pupilcoordinates of −1.5 mm, 0 mm and +1.5 mm at an angle of view of (X,Y)=(0°, 0°). In FIG. 19, it is shown how the dominant diffractionwavelength shifts according to the angle of view, while in FIG. 20, itis shown how the dominant diffraction wavelength shifts according to thepupil coordinates. In this concrete example, since the light source iscloser to the pupil than in the first working configuration, adiffraction wavelength shift within the pupil plane also occurs.

In FIGS. 19 and 20, the emission spectra of the corresponding Rwavelength regions (among the respective wavelength regions of the LED 3shown in FIG. 27) are also superimposed. In actuality, the quantity oflight that reaches the eye of the observer (i.e., the brightness) is aproduct of these two types of graphs (i.e., a product of the diffractionefficiency and the emission spectrum of the R wavelength region). Thebrightness distribution within the screen is shown in FIG. 21, and thebrightness distribution within the pupil plane is shown in FIG. 22. Therespective plotted points in FIG. 21 correspond to the product of thepeaks of the diffraction efficiency at the respective angles of view inFIG. 19 and the intensity of the light emitted from the LED 3 at thecorresponding peak wavelengths. The respective plotted points in FIG. 22correspond to the product of the peaks of the diffraction efficiency atthe respective pupil coordinates in FIG. 20 and the intensity of thelight emitted from the LED 3 at the corresponding peak wavelengths.

In the present concrete example, the respective ratios λ_(yr)/λ_(or) ofthe dominant diffraction wavelength λ_(yr) at angles of view of −5° and+50 to the dominant diffraction wavelength λ_(or) at the center of theangle of view are 1.016 and 0.979, and are thus less than 0.98 andgreater than 1.013, so that the conditions of Equation (22) and Equation(23) described above are satisfied. As a result, the intensity withinthe pupil plane is close to flat as shown in FIG. 22.

Furthermore, the differences |λ_(yr)−λ_(or)| between the dominantdiffraction wavelengths in the center and periphery of the angle of vieware 9.87 and 13.16, respectively, and the full width at half maximumFWHMr of the light source used in the present concrete example is 23 nm;accordingly, when the value of the right side of Equation (24) iscalculated, respective values of 0.43 and 0.57 are obtained at angles ofview of −5° and +5°, so that the conditions of Equation (24) aresatisfied. As a result, a balanced brightness is obtained both withinthe pupil plane and within the screen, as is shown in FIGS. 21 and 22.

Furthermore, the difference between the angle θ1 r of the referencelight source and the angle of incidence θ2 of the optical axis of theray tracing is 2.9°, so that the conditions of Equation (25) aresatisfied.

[Fourth Working Configuration]

Although this is not shown in the figures, the image display deviceconstituting a fourth working configuration of the present invention isa device in which the image display device constituting a concreteexample of the first working configuration described above is modifiedas follows.

The only difference between the image display device of the presentworking configuration and the image display device of the concreteexample of the first working configuration described above is theconstruction of the reflective type HOE 6. In the present workingconfiguration, the reflective type HOE 6 is an HOE in which thereflective type HOE of the concrete example of the first workingconfiguration described above (G reflective type HOE), the reflectivetype HOE of the concrete example of the second working configurationdescribed above (B reflective type HOE) and the reflective type HOE ofthe concrete example of the third working configuration described above(R reflective type HOE) are superimposed in three layers. Furthermore,as in the first working configuration described above, the LED 3 used inthe present working configuration is also an LED which has threewavelength regions, and which has the emission spectrum shown in FIG.27.

When the light of the three wavelength regions from this LED 3 passesthrough the image display element 2, the single display unit of theimage display element may be spatially divided into three parts so thatdots respectively corresponding to R, G and B are formed, and so thatcorresponding images are displayed, or this display unit may be dividedin terms of time so that images respectively corresponding to R, G and Bare switched and displayed (for example) every 1/90 second, and so thatthe timing of the light emission of the three wavelength regions of theLED is synchronized with this. Furthermore, the image information of therespective wavelength regions is subjected to a diffraction effect andan image focusing effect by the corresponding layers of the HOE, andfull-color images are obtained by additive color mixing after this lightis conducted to the pupil of the observer.

The brightness characteristics in the image plane and the brightnesscharacteristics in the pupil plane of the reflective type HOE 6 used inthe present working configuration, i.e., a reflective type HOE which hasa structure in which the reflective type HOEs of the concrete examplesof the first through third working configurations are superimposed arerespectively shown in FIGS. 23 and 24. In FIGS. 23 and 24, the verticalaxes show the brightness, which is the product of the diffractionefficiency and light emission intensity of the LED; these values arenormalized with the brightest value being taken as 1.

As is seen from FIG. 23, since the ratios of the three colors aresubstantially the same within the screen, observation with a good colorbalance is possible throughout the entire region of the image.Furthermore, as is seen from FIG. 24, with regard to the pupil plane, areduction in red light is seen in the direction in which the pupilcoordinate Py is positive; however, blue and green are substantiallyflat. Accordingly, there is merely some variation in the degree ofredness with respect to movements of the eye of the observer; there isno abrupt decrease in brightness.

Respective working configurations of the present invention, and concreteexamples of these working configurations, were described above. However,the present invention is not limited to these working configurations orconcrete examples.

For instance, the respective working configurations described above wereexamples in which a head-mounted image display device was constructedusing the image combiner of the present invention. However, therespective image combiners 1 used in the respective workingconfigurations described above could also be constructed so as to allowmounting on the ocular lens parts of camera view finders, microscopesand binoculars, or these image combiners could also be incorporated intocameras, microscopes, binoculars, or the like.

Furthermore, the respective working configurations described above wereexamples in which the present invention was applied to a see-throughtype head-mounted image display device; however, the present inventioncan also be applied to image display devices that are not of thesee-through type. In this case, the image display devices of therespective working configurations described above can be constructed sothat light from the outside world is not incident on the image combiner1. In such a case, since the part constituting the image combiner 1 doesnot superimpose two images, this part cannot be called an imagecombiner; instead, this part constitutes a light conducting part thatconducts light from the image display element 2 to the eye of the user.In this case, the lower portion of the plate-form part (portion belowthe HOE 6) in the image combiner 1 may be removed. For example, such animage display device that is not of the see-through type can beinstalled inside the flipper part of a portable telephone in the samemanner as in the case of Japanese Patent Application Kokai No.2001-264682.

1. An image combiner in which a reflective type hologram optical elementis installed, and light from the outside world is superimposed on lightfrom image display means, this image combiner being characterized inthat the light that is emitted from the image display means haswavelength region components that respectively extend before and afterone or more peak wavelengths, and the wavelength λ_(o) and wavelengthλ_(y) are different where λ_(o) is the wavelength at which thediffraction efficiency shows a maximum value in the wavelength region inthe vicinity of a single peak wavelength among the one or more peakwavelengths after the chief rays that are emitted from the center of thedisplay part of the image display means are diffracted by the reflectivetype hologram optical element, and λ_(y) is the wavelength at which thediffraction efficiency shows a maximum value in the wavelength region inthe vicinity of this single peak wavelength among the one or more peakwavelengths after the chief rays that are emitted from the peripheralportions of the display part are diffracted by the reflective typehologram optical element.
 2. The image combiner according to claim 1,wherein either Equation (6) or Equation (7) shown below is satisfied:1.013<λ_(y)/λ_(o)  (6).λ_(y)/λ_(o)<0.98  (7).
 3. The image combiner according to claim 1,wherein Equation (8) shown below is satisfied where FWHM is the fullwidth at half maximum for the single peak wavelength of the light thatis emitted from the image display means:0.2<|(λ_(y)−λ_(o))/FWHM|  (8).
 4. The image combiner according to claim1, wherein Equation (9) shown below is satisfied where θ1 is the angleof incidence (angle calculated in air) on the center of the reflectivetype hologram optical element from the light source that is located onthe side of the eye of the observer during playback among the two lightsources used to expose the reflective type hologram optical elementcorresponding to the single wavelength region or the one of peakwavelength regions during the manufacture of this element, and θ2 is theangle of reflection (angle calculated in air) at the reflective typehologram optical element of the light rays that are emitted from thecenter of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner:0.80<|θ1−θ2|  (9).
 5. An image display device comprising the imagecombiner according to claim 1, and an image display means, wherein atleast a part containing the image combiner is mounted on a user duringuse.
 6. An image display device comprising image display means and alight conducting part that conducts light from the image display meansto the eye of the user, this image display device being characterized inthat: the light conducting part has a reflective type hologram opticalelement, the light that is emitted from the image display means haswavelength region components that respectively extend before and afterone or more peak wavelengths, and the wavelength λ and wavelength λ_(y)are different where λ_(o) is the wavelength at which the diffractionefficiency shows a maximum value in the wavelength region in thevicinity of a single peak wavelength among the one or more peakwavelengths after the chief rays that are emitted from the center of thedisplay part of the image display means are diffracted by the reflectivetype hologram optical element, and λ_(y) is the wavelength at which thediffraction efficiency shows a maximum value in the wavelength region inthe vicinity of the single peak wavelength after the chief rays that areemitted from the peripheral portions of the display part are diffractedby the reflective type hologram optical element.
 7. The image displaydevice according to claim 6, wherein either Equation (6) or Equation (7)shown below is satisfied:1.013<λ_(y)/λ_(o)  (6)λ_(y)/λ_(o)<0.98  (7).
 8. The image display device according to claim 6,wherein Equation (8) shown below is satisfied where FWHM is the fullwidth at half maximum for the single peak wavelength of the light thatis emitted from the image display means:0.2<|(λ_(y)−λ_(o))/FWHM|  (8).
 9. The image display device according toclaim 6, wherein Equation (9) shown below is satisfied where θ1 is theangle of incidence (angle calculated in air) on the center of thereflective type hologram optical element from the light source that islocated on the side of the eye of the observer during playback among thetwo light sources used to expose the reflective type hologram opticalelement (corresponding to the single wavelength region or the one ofpeak wavelength regions during the manufacture of this element, and θ2is the angle of reflection (angle calculated in air) at the reflectivetype hologram optical element of the light rays that are emitted fromthe center of the display part of the image display means and directedtoward the center-of the exit pupil of the image combiner:0.8°<|θ1−θ2|  (9).
 10. The image display device according to claim 7,wherein Equation (8) shown below is satisfied where FWHM is the fullwidth at half maximum for the single peak wavelength of the light thatis emitted from the image display means:0.2<|(λ_(y)−λ_(o))/FWHM |  (8).
 11. The image display device accordingto claim 10, wherein Equation (9) shown below is satisfied where θ1 isthe angle of incidence (angle calculated in air) on the center of thereflective type hologram optical element from the light source that islocated on the side of the eye of the observer during playback among thetwo light sources used to expose the reflective type hologram opticalelement (corresponding to the single wavelength region or the one ofpeak wavelength regions during the manufacture of this element, and θ2is the angle of reflection (angle calculated in air) at the reflectivetype hologram optical element of the light rays that are emitted fromthe center of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner:0.80<|θ1−θ2  (9).
 12. The image display device according to claim 8,wherein Equation (9) shown below is satisfied where θ1 is the angle ofincidence (angle calculated in air) on the center of the reflective typehologram optical element from the light source that is located on theside of the eye of the observer during playback among the two lightsources used to expose the reflective type hologram optical element(corresponding to the single wavelength region or the one of peakwavelength regions during the manufacture of this element, and θ2 is theangle of reflection (angle calculated in air) at the reflective typehologram optical element of the light rays that are emitted from thecenter of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner:0.80<|θ1−θ2|  (9).
 13. The image display device according to claim 7,wherein Equation (9) shown below is satisfied where θ1 is the angle ofincidence (angle calculated in air) on the center of the reflective typehologram optical element from the light source that is located on theside of the eye of the observer during playback among the two lightsources used to expose the reflective type hologram opticalelement-(corresponding to the single wavelength region or the one ofpeak wavelength regions during the manufacture of this element, and θ2is the angle of reflection (angle calculated in air) at the reflectivetype hologram optical element of the light rays that are emitted fromthe center of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner:0.8°<|θ1−θ2|  (9).
 14. The image combiner according to claim 2, whereinEquation (8) shown below is satisfied where FWHM is the full width athalf maximum for the single peak wavelength of the light that is emittedfrom the image display means:0.2<|(λ_(y)−λ_(o))/FWHM|  (8).
 15. The image combiner according to claim14, wherein Equation (9) shown below is satisfied where θ1 is the angleof incidence (angle calculated in air) on the center of the reflectivetype hologram optical element from the light source that is located onthe side of the eye of the observer during playback among the two lightsources used to expose the reflective type hologram optical elementcorresponding to the single wavelength region or the one of peakwavelength regions during the manufacture of this element, and θ2 is theangle of reflection (angle calculated in air) at the reflective typehologram optical element of the light rays that are emitted from thecenter of the display part of the image display means and directedtoward the center of the exit pupil of the image combiner:0.8°<|θ1−θ2|  (9).
 16. The image combiner according to claim 2, whereinEquation (9) shown below is satisfied where θ1 is the angle of incidence(angle calculated in air) on the center of the reflective type hologramoptical element from the light source that is located on the side of theeye of the observer during playback among the two light sources used toexpose the reflective type hologram optical element corresponding to thesingle wavelength region or the one of peak wavelength regions duringthe manufacture of this element, and θ2 is the angle of reflection(angle calculated in air) at the reflective type hologram opticalelement of the light rays that are emitted from the center of thedisplay part of the image display means and directed toward the centerof the exit pupil of the image combiner:0.80<|θ1−θ2  (9).
 17. The image combiner according to claim 3, whereinEquation (9) shown below is satisfied where θ1 is the angle of incidence(angle calculated in air) on the center of the reflective type hologramoptical element from the light source that is located on the side of theeye of the observer during playback among the two light sources used toexpose the reflective type hologram optical element corresponding to thesingle wavelength region or the one of peak wavelength regions duringthe manufacture of this element, and θ2 is the angle of reflection(angle calculated in air) at the reflective type hologram opticalelement of the light rays that are emitted from the center of thedisplay part of the image display means and directed toward the centerof the exit pupil of the image combiner:0.80<|θ1−θ2  (9).
 18. An image display device comprising the imagecombiner according to claim 2, and an image display means, wherein atleast a part containing the image combiner is mounted on a user duringuse.
 19. An image display device comprising the image combiner accordingto claim 3, and an image display means, wherein at least a partcontaining the image combiner is mounted on a user during use.
 20. Animage display device comprising the image combiner according to claim 4,and an image display means, wherein at least a part containing the imagecombiner is mounted on a user during use.